vào thời đó 
at that time, in those times, in those days [ vào ] : at, on (date), in, to; to enter, go in, access
[ thời ] : time(s), era
[ đó ] : that, those, there, that
Most Common Compounds Set 1:
Most Common Compounds Set 2 :
vào thời đó at that time, in those times, in those days